Emplacement and deformation of the Vinukonda meta-granite (Eastern Ghats, India) -: Implications for the geological evolution of peninsular India and for Rodinia reconstructions

The U-Pb and Rb-Sr systematics of zircon populations from two samples and biotite-white mica pairs from four samples constrain the time of emplacement and deformation of the Vinukonda meta-granite, Eastern Ghats, India. Sm-Nd and Lu-Hf systematics of whole rock samples provide information on the magma source and its evolution. The granitic magma intruded into granitic gneisses of the Vinjamuru domain (Krishna Province, Andhra Pradesh, India), which were already deformed and metamorphosed at epidote-amphibolite facies peak conditions. Consistent Sm-Nd and Lu-Hf whole rock model ages suggest an isotopically homogeneous crustal source and a multi-stage evolution of the granitic magma. U-Pb analyses of prismatic zircon multi-grain fractions define two discordias with identical upper intercepts at 1588.4 +/- 7.1 and 1589.7 +/- 15.7 Ma, interpreted to date magma emplacement. Rb-Sr ages of strongly annitic biotite (X-Mg 0.07-0.20) and phengitic white mica (3.13-3.23 Si pfu) show a complex age pattern. Due to low temperatures during deformation, the Rb-Sr system only partly re-equilibrated in biotite. Synkinematically grown phengitic white mica evidence a low-grade metamorphic overprint at 501-474 Ma. The deformation was associated with W/NW-directed nappe stacking, which caused the actual geological configuration of southern Andhra Pradesh with the arcuate Nallamalai fold belt as most prominent feature. Regional considerations lead to the proposition that thrusting in the Krishna Province is the expression of intracratonic deformation in response to the amalgamation of the Eastern Ghats-Rayner Province terrane with subcontinental India in early Palaeozoic time. (c) 2006 Elsevier B.V. All rights reserved.